JP-A-2004-36543 discloses a device for purifying exhaust gas equipped with an oxidizing catalyst and a diesel particulate filter (hereinafter referred to as “DPF”) in the downstream of the oxidizing catalyst. In this device for purifying exhaust gas, NO in the exhaust gas is oxidized into NO2 by the oxidizing catalyst and the DPF continuously oxidizes, burns and removes particulates by utilizing NO2 as an oxidizing agent. In this device for purifying exhaust gas, when the amount of particulates deposited on the DPF have exceeded a predetermined amount, HC (hydrocarbons) are fed to the oxidizing catalyst and burned on the oxidizing catalyst to elevate the temperature of the exhaust gas, i.e., to elevate the temperature of the DPF, thereby particulates deposited on the DPF are oxidized, burned and removed.
Concerning the device for purifying exhaust gas disclosed in JP-A-2004-36543, the oxidizing catalyst often adsorbs HC while HC are being fed to the oxidizing catalyst. If HC are adsorbed in large amounts by the oxidizing catalyst, HC may rapidly burn to thermally deteriorate the oxidizing catalyst. Therefore, the device for purifying exhaust gas disclosed in JP-A-2004-36543 has been so designed as to feed HC in decreased amounts to the oxidizing catalyst or to discontinue the feed of HC to the oxidizing catalyst when HC are adsorbed by the oxidizing catalyst in amounts in excess of a predetermined value.